1. Field of the Invention
The present invention relates generally to semiconductor fabrication and, more particularly, to systems and methods for detecting watermark formations on semiconductor wafers.
2. Description of Related Art
Semiconductor fabrication involves various “wet” and “dry” processing steps. Examples of wet processes include: patterning via wet etching or chemical-mechanical polishing, contamination removal, liquid-emersion inspection, and the like. Meanwhile, examples of dry processes include: dry etching, removal of liquids from the surface of the wafer, and the like. Insufficient drying of the wafer, especially after a wet process, generally leads to the formation of watermarks on the wafer's surface.
One process that leads to the formation of watermarks may be generally described as follows. First, a semiconductor wafer undergoes a wet processing step and water droplets are formed on its surface. Then, oxygen from the air dissolves into the water droplet. The oxygen dissolved in the droplet reacts with silicon from the wafer to form SiO2. The silicon oxide interacts with hydrogen within the water droplet and produces H2SiO3. When the water droplet evaporates, H2SiO3 residues remain on the wafer surface.
Depending upon the size of the watermark formations in relation to the size of device features fabricated on the wafer, the watermarks may result in manufacturing defects. And, with the increasingly reduced size of device features currently being fabricated, the presence of watermarks, however diminutive, presents a serious concern. U.S. Pat. No. 5,932,493 (the '493 patent) discusses a method for minimizing watermarks on silicon substrates. In essence, the '493 proposes preventing the formation of watermarks by rinsing silicon wafers in an organic solvent prior to drying.